1. Field of the Invention
The present invention relates to a monitor system for a hierarchical network in which routers are organized in a tree structure and local network nodes are polled at intervals from the routers.
2. Description of the Related Art
In a network monitor system as disclosed in Japanese Laid-Open Patent Specification Hei-7-23054, a network monitor is connected to a number of data transmission units via a line connection unit in which a number of polling circuits are associated with the data transmission units to perform polling operations under control of the network monitor to collect data from the polled units. The data collected in this manner are stored in a memory of the line connection unit and the network monitor reads the contents of the memory at regular intervals. While this polling technique is useful for reducing the amount of task performed by the network monitor, the polling traffic accounts for a substantial proportion of the overall network traffic if the polling rate is increased.
According to another prior art network monitor system as disclosed in Japanese Laid-Open Patent Specification Hei-6-37782, repeater stations are connected in a hierarchical tree structure with the top of the structure being connected to a network monitor. The network monitor uses data representing the structural organization of the network to poll the repeater stations, starting with the stations at the lowest level of the hierarchy. If the polling to a station at the lowest level is successful, the network monitor cancel its polling to a station immediately higher than the lowest-level station. However, the cancellation of polling to intermediate-level stations would have no effect on reducing the total traffic if many lowest-level stations were attached to the intermediate-level stations.
It is therefore an object of the present invention to provide a network monitor system in which the polling traffic is reduced by polling silent network nodes.
According to a first aspect, the present invention provides a communication network comprising a plurality of routers interconnected in a hierarchical tree structure, a plurality of local network nodes connected to each of the routers located at lowest level of the tree structure, and a network monitor connected to one of the routers which is located at top of the tree structures. Each of the routers comprises polling means for detecting a low activity local network node having no access from the network for a period longer than a predetermined length and polling the local network node to receive a response therefrom indicating an operating state of the polled node, and a memory for storing the response. The network monitor transmits a polling signal to each router at the lowest level and receiving contents of the memory. Since the polling from each router to its own local network nodes is performed only to those nodes which remain silent for a predetermined period or longer, the polling traffic of the network is significantly reduced.
According to a second aspect, the present invention provides a communication network comprising a plurality of routers interconnected in a hierarchical tree structure, a plurality of local network nodes connected to each of the routers located at lowest level of the tree structure, and a network monitor connected to one of the routers which is located at top of the tree structure. Each of the routers comprises a first, or cache memory having a plurality of entries, address resolution means for mapping a physical address to a corresponding logical address in one of the entries and setting a predetermined timer value in the one entry in response to a packet from the network, and varying the timer value a predetermined amount at regular intervals, polling means for making a search through the first memory at regular intervals to detect an entry whose timer value is varied to a predefined threshold and polling one of the local network nodes corresponding to this entry to receive a response therefrom indicating an operating state of the polled node, and a second memory for storing the response. The network monitor transmits a polling signal to each router at the lowest level of the tree structure and receives the contents of the second memory.